Gas chromatography is a well known technique that is extensively used in quantitative analysis. However, in analyses involving nitrogen compounds, particularly nitrogen oxides, gas chromatography has provided results that are unreliable. Oxides of nitrogen, expecially nitrogen dioxide, are very reactive and at trace levels tend to be irreversibly absorbed, and thereby lost, on surfaces of storage containers, transfer lines, column packing materials, and the like. As a consequence the integrity of samples containing nitrogen oxides is often questionable, especially after storage or transfer is attempted.
Because of the concern in recent years of the impact of nitrogen oxides upon the environment, it has become important to provide an accurate and reliable method for their analysis. A widely used method for analysis of nitrogen oxides is based on chemiluminescence. While this technique is quite sensitive, it has a definite drawback in that it must be calibrated with mixtures of trace levels or reactive, difficult to store oxides of nitrogen. The accuracy with which these supposedly "standard" mixtures can be prepared is not very high and the integrity of standard gases after storage and transfer is often in question.
O. Grubner and A. S. Goldin in Analytical Chemistry, 45, 944 (May 1973), describe work in which styrene was used as a gas phase reactant with nitrogen dioxide. Five chromatographic peaks were observed. The authors concluded that the five peaks were not nitrated styrene derivatives but were probably cleaved fragments of the styrene because their retention times were shorter than styrene itself. When more than three products are formed, it is difficult, if not impossible, to make quantitative measurements because each compound produces a different size response in the chromatographic detector and small changes in reaction conditions can cause large changes in the ratios of the products produced. The authors state that they also studied reactions between nitrogen dioxide and benzene, toluene, xylene, pentene, 1,1-dimethylhydrazine and triethanolamine. However, they found that with their method only the reaction with xylene produced significant quantities of compounds that could be detected by an electron capture detector.
It is an object of this invention to provide an improved process for the qualitative and quantitative analysis of nitrogencontaining compounds.
Another object of the invention is to provide a gas chromatographic process for analysis of oxides of nitrogen in ambient air and nitrates and nitrites in an aqueous medium and in aerosols.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure and the drawing, in which: